Referencing systems in the sense of this application are known for example from DE 196 39 615 C2, the content of the disclosure of which is explicitly incorporated by way of reference in the present application. Such systems, also known as navigation systems, provide the connection between the surgeon carrying out the treatment, i.e. the patient anatomy as the surgeon sees it during treatment, and diagnostic data obtained for example from computer tomography and represented visually by an image output via a computational unit. For detecting three-dimensional spatial co-ordinates, a plurality of markers with known dimensions are used, such as are for example described in DE 196 39 615 C2, line 2. A radiation source, in particular an infrared radiation source, illuminates the area in which three-dimensional spatial co-ordinates are to be detected, and the radiation reflected by the markers is detected with the aid of at least two cameras, each from a different angle of view. Alternatively, the objects to be referenced can also actively emit radiation, in particular infrared radiation, to which end radiation sources, for example LEDs, are attached to the objects, the radiation from which is detected as described above. The camera signals are evaluated with the aid of a subordinated computational unit and by means of known algorithms.
It is necessary for referencing for there to always be at least two cameras monitoring the area in which three-dimensional spatial co-ordinates are to be detected, from different angles of view, without the relevant field of view of the cameras being obscured. Here, it is desirable for the at least two cameras to be adjustable in the simplest way possible, in accordance with the respective circumstances.
To this end, DE 196 39 615 C2 discloses two cameras held by a common frame which have to be positioned laterally above the setting to be detected, for example the operating table. In certain situations, this can be difficult. In an operating theater, the suitable position for the cameras of the referencing system depends in particular on the positions at which the operating staff are standing around the operating table, and on where apparatus which could obscure the field of view of the cameras is positioned. It must be taken into account here that different operations may require different apparatus and positions. Suitably positioning and aligning the cameras is thus comparatively difficult.
In other referencing systems, the cameras are therefore either suspended from the ceiling of the operating theater or attached at other suitable points in the operating theater, for example to the computer itself or in the corners of the room. It can nonetheless easily transpire that the field of view of one or more may be obscured at the same time, making accurate referencing impossible. Positioning the cameras at a comparatively long distance from the relevant area in which three-dimensional spatial co-ordinates are to be detected also has the disadvantage that a comparatively large amount of zero order information is detected by the cameras, which can compromise the referencing accuracy, or at least unnecessarily increases the computational demands involved.